At least some known rotary machine, such as gas turbine engines, typically include squeeze film dampers that provide damping to rotating components, such as a rotor shaft, to reduce and control vibration. At least some known squeeze film dampers include a bearing support member, such as an outer race of a rolling element bearing supported shaft, fitted within an annular housing chamber that restricts radial motion of the bearing support member. An annular film space is defined between an outer surface of the outer race and an opposite inner surface of the bearing housing such that damper oil can be introduced therein. Vibratory and/or radial motion of the shaft and its bearing generate hydrodynamic forces in the damper oil within the annular film space that result in damping forces causes by the movement of the shaft.
In known squeeze film damper systems, the provided damping is generally consistent during engine start conditions and during engine cruising operating conditions. However, gas turbine engines typically require a greater amount of damping during engine start conditions, such as during bowed rotor starts, rather than during normal gas turbine engine cruising conditions when excess damping can decrease engine efficiency.